The Quantum Structure of the Atom

Abstract

The earlier chapters have discussed the interaction between electromagnetic radiation and a free charged particle (electron). In the last chapter it was found that, when the classical description is compared with observations from experiment, it becomes necessary to introduce certain quantum rules. We must now turn to the interaction between electromagnetic radiation and an electron bound in an atom (or molecule or condensed matter). Presumably the same rules of interaction apply—the energy of the state of the atom is changed by hv,and the angular momentum of the state is changed by h/2π. The other rule, concerning the change of linear momentum, can be neglected in most circumstances. Of course a change of momentum does occur but, since the atom is considerably more massive than the electron, the observable effects are small. Mention will be made from time to time, however, of momentum change. The more noticeable changes are in those properties that are intrinsic to the internal structure of the atom—its internal state of energy and its internal state of angular momentum.